When silver halide photographic products are developed with a photographic developer, the chemical composition of the developer changes over time (consumption of chemical products), necessitating the use of replenishment solutions. These replenishment solutions make it possible to maintain effective concentrations of chemical compounds in the developer.
During development, another phenomenon disturbs the composition of the developer and consequently its effectiveness. This is because, during the development of silver halide photographic products, the developer becomes enriched with halide ions coming from the photographic product. When these ions are bromide or iodide ions, they considerably slow down the image development speed.
These developers whose chemical composition has been changed through use are called "seasoned developers".
Developers initially contain a certain quantity of bromide; an additional quantity of bromide or iodide ions is released during development. It is important to maintain the bromide or iodide concentration of the developer within certain limits. Otherwise, the bromide or iodide concentration in the developer would increase continuously, which would rapidly make the developer unusable.
It is already known that the bromide or iodide ions released during development in dye coupling developers can be removed with an ion exchange resin.
EP-A-178539 describes a method for treating a seasoned developer with an anion exchanger which contains OH groups as exchangeable groups.
The article "Developer recycling--A new generation", H. Meckl, Journal of Imaging Technology, 13, 1987, 3, 85-89, describes a system in which the effluent at the outlet of the developing tank is poured into a holding tank. It then passes through an ion exchange resin in order to remove the bromide ions. Regenerating chemicals are added to this effluent, now devoid of bromide ions. The replenisher/regenerated solution thus obtained can be re-used as a developer.
EP-A-609940 describes a method for treating a silver halide photographic product in which the seasoned developer is treated in order to remove the seasoning ions. Then a quantity of maintenance compounds is added which is sufficiently small not to cause an overflow. The method is characterized in that the seasoned developer is treated with means which make it possible to remove in a continuous manner all the bromide ions and to maintain this zero concentration during the processing of photographic films. According to this reference, bromide ions can be removed by means of ion exchange resins. These resins are of the anionic, strongly basic type. The preferred resins being resins of the anionic type consisting of a polystyrene matrix cross-linked, for example, with divinylbenzene, comprising quaternary ammonium groups.
Also, in the noted reference, the affinity of the resins with respect to bromide, sulfite and sulfate was studied by treating a KODAK Process C-41 color developer. However, it gives no indication as to the performance of the system or the affinity of the resins which can be used.
Although these techniques for treating seasoned developers with ion exchange resins are known, it is impossible to choose from the commercially available resins an ion exchange resin which is particularly appropriate for treating a particular developer. The technical information for the different commercial resins contains only general indications of structure or a particular application. Anionic resins, cationic resins, acrylic resins, styrene resins, cross-linked or not, for example, cross-linked with divinylbenzene, do exist. These resins can be of the gel type that have a natural porosity, or of the macroporous type to which are added, when polymerization takes place, a pore-forming substance that forms an artificial porosity inside the resin.
Ion exchange resins are generally developed for the treatment of water. The diversity and concentration of ions in water are not comparable to those of the different ions present in a photographic developer.
Moreover, there are a large number of photographic developers, for example, dye coupling developers, hydroquinone developers, ascorbic acid developers, etc. These developers have complex and very different chemical compositions, and they contain a large number of ionic and organic substances in very variable quantity. The presence of organic compounds can rapidly cause poisoning of the resin, which is then ineffective in retaining ionic substances, particularly bromide ions.
It is because of this lack of selectivity of resins that it is impossible to use them to treat a black-and-white developer containing hydroquinone. In addition, the selectivity of the resins is dependent on the concentration of the different ions contained in the solution to be treated.
If these different developers are to be treated by means of anion exchange resins, the problem is to choose an effective resin from those available.
A person skilled in the art who wishes to develop a system for treating an ascorbic acid photographic developer in order to avoid the effects of seasoning has no choice but to test a large number of anion exchange resins in order to choose the most effective one.
It is indeed desirable to be able to identify in a simple and economical manner ion exchange resins which, when they are used for the treatment of a seasoned ascorbic acid developer, have improved effectiveness, that is to say a resin making it possible to treat, for a given volume, a larger volume of developer.
Certain resins have an improved effectiveness in removing bromide ions in the treatment of ascorbic acid developers, and this improved effectiveness is closely linked with the affinity of this resin for bromide ions in the presence of carbonate ions, even when the concentration of carbonate ions is much higher than the concentration of bromide ions.